From: Alberto Garcia <berto@igalia.com>
To: Kevin Wolf <kwolf@redhat.com>, Maxim Levitsky <mlevitsk@redhat.com>
Cc: vsementsov@virtuozzo.com, qemu-block@nongnu.org,
zhang_youjia@126.com, qemu-devel@nongnu.org,
Max Reitz <mreitz@redhat.com>,
andrey.shinkevich@virtuozzo.com
Subject: Re: [PATCH 1/1] Fix qcow2 corruption on discard
Date: Mon, 23 Nov 2020 19:20:00 +0100 [thread overview]
Message-ID: <w51mtz8541b.fsf@maestria.local.igalia.com> (raw)
In-Reply-To: <20201123160941.GD5317@merkur.fritz.box>
On Mon 23 Nov 2020 05:09:41 PM CET, Kevin Wolf wrote:
>> Commit 205fa50750 ("qcow2: Add subcluster support to zero_in_l2_slice()")
>> introduced a subtle change to code in zero_in_l2_slice:
>>
>> It swapped the order of
>>
>> 1. qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
>> 2. set_l2_entry(s, l2_slice, l2_index + i, QCOW_OFLAG_ZERO);
>> 3. qcow2_free_any_clusters(bs, old_offset, 1, QCOW2_DISCARD_REQUEST);
>>
>> To
>>
>> 1. qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
>> 2. qcow2_free_any_clusters(bs, old_offset, 1, QCOW2_DISCARD_REQUEST);
>> 3. set_l2_entry(s, l2_slice, l2_index + i, QCOW_OFLAG_ZERO);
Ouch :( Good catch!
>> - qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
>> if (unmap) {
>> qcow2_free_any_cluster(bs, old_l2_entry, QCOW2_DISCARD_REQUEST);
>> }
>> set_l2_entry(s, l2_slice, l2_index + i, new_l2_entry);
>> + qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
>
> Good catch, but I think your order is wrong, too. We need the original
> order from before 205fa50750:
>
> 1. qcow2_cache_entry_mark_dirty()
> set_l2_entry() + set_l2_bitmap()
>
> 2. qcow2_free_any_cluster()
I agree with Kevin on this.
Berto
next prev parent reply other threads:[~2020-11-23 18:21 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-23 15:49 [PATCH 0/1] Fix qcow2 corruption after addition of subcluster support Maxim Levitsky
2020-11-23 15:49 ` [PATCH 1/1] Fix qcow2 corruption on discard Maxim Levitsky
2020-11-23 16:09 ` Kevin Wolf
2020-11-23 18:20 ` Alberto Garcia [this message]
2020-11-23 18:23 ` Maxim Levitsky
2020-11-23 17:38 ` Kevin Wolf
2020-11-23 18:11 ` Maxim Levitsky
2020-11-24 9:17 ` Kevin Wolf
2020-11-24 18:59 ` Alberto Garcia
2020-11-24 18:59 ` Maxim Levitsky
2020-11-24 19:44 ` Maxim Levitsky
2020-11-25 16:49 ` Alberto Garcia
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